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Hibernation requires balancing energy and water demands over several months. Many studies have noted the importance of fat for hibernation energy budgets, but protein catabolism in hibernation has received less attention, and whole-animal changes in lean mass have not previously been considered. We used quantitative magnetic resonance body composition analysis to measure deposition of fat and lean mass of cave myotis (

Many migratory bats require forested sites for roosting and foraging along their migration path, but increased urbanization and intensive agricultural practices may reduce the availability of stopover sites. Urban forests may provide important stopover habitat, maintaining landscape connectivity in regions where the majority of natural habitat has been cleared for development. Island biogeography theory can be applied to urbanized temperate forest biomes where small urban forests represent islands separated from the larger “mainland” forest. We used acoustic monitoring during the fall migration period to investigate the use of urban forest habitat by a migratory species, the silver-haired bat (Lasionycteris noctivagans (Le Conte, 1831)). We predicted that recorded activity would have a positive relationship with forest patch area and shape and a negative relationship with isolation from other forest patches, as suggested by island biogeography theory. We observed greater activity at larger forest patches, and although relationships for shape and isolation were not statistically supported, the observed patterns were consistent with predictions. Our results demonstrate the need for more in-depth research on the habitat requirements for both migratory and resident bat species and the impact that ongoing urbanization has on local bat populations.

Hibernators adjust the expression of torpor behaviourally and physiologically to balance the benefits of energy conservation in hibernation against the physiological and ecological costs. Small fat-storing species, like many cave-hibernating bats, have long been thought to be highly constrained in their expression of hibernation because they must survive winter relying only on endogenous energy stores. We evaluated behavioural microclimate selection in tri-colored bats (Perimyotis subflavus (F. Cuvier, 1832)) across a 3-month hibernation experiment under laboratory conditions. We also opportunistically tested for evidence of acclimatization in torpid metabolic rate (TMR). When given access to gradients in microclimate, bats tended to choose the warmest temperature available (11 °C) while almost completely avoiding the driest condition available (85% relative humidity at 8 °C). Furthermore, bats held at different temperatures over the course of the hibernation showed no differences in TMR when measured under common conditions at the end of hibernation. Taken together, our results suggest that selective pressures to conserve energy during hibernation are not overwhelmingly strong and further support the proposition that optimal expression of hibernation is something less than the maximal expression of hibernation unless the animal is nearing starvation.

In this contribution to Dr. Brock Fenton's Festschrift, we briefly reflect on Dr. Fenton's seminal works examining bat swarming behaviour in Ontario and use these reflections as a launch pad to conduct a global review on autumn swarming in bats, and underlying hypotheses to explain this behaviour. Our review frames the swarming period as a time of critical transitions, during which bats must balance multiple life history trade-offs, and we consider how various intrinsic and extrinsic factors may contribute to inter- and intraspecific differences in autumn behaviour. We discuss the transition away from summer residency, including maternity colony breakup, day roosting, and migration during autumn. We review key life history elements of swarming, including mating behaviours and associated reproductive condition, genetic exchange during swarming, and variation among sexes, ages, and species. Finally, we discuss the behaviours and physiological states of bats transitioning from the swarming period to hibernation. Throughout, we identify common patterns and also exceptions. Over 50 years of research has yielded many insights into autumn swarming, but knowledge gaps remain. Future research focus on a greater diversity of species will reveal general principles underlying the transition from summer active season, through the swarming period, and into winter hibernation.

Migratory connectivity is the degree to which populations are linked in space and time across the annual cycle. Low connectivity indicates mixing of populations while high connectivity indicates population separation in space or time. High migratory connectivity makes individual populations susceptible to local environmental conditions; therefore, evaluating migratory connectivity continuously across a species range is important for understanding differential population trends and revealing places and times contributing to these differences. The common nighthawk Chordeiles minor is a widespread, declining, long‐distance migratory bird. Variable population trends across the nighthawk breeding range suggest that knowledge of migratory connectivity is needed to direct conservation. We used GPS tags to track 52 individuals from 12 breeding populations. We estimated migratory connectivity as 0.29 (Mantel coefficient: 0 = no connectivity, 1 = full connectivity) between the breeding and wintering grounds. We then estimated migratory connectivity at every latitude (spatial connectivity) or day (temporal connectivity) of migration and smoothed those migratory connectivity estimates to produce continuous migratory connectivity ‘profiles'. Spatial and temporal connectivity were highest during migration through North America (around 0.3–0.6), with values generally around 0 in Central and South America due to mixing of populations along a common migratory route and similar migration timing across populations. We found local peaks in spatial and temporal connectivity during migration associated with crossing the Gulf of Mexico. We used simulations to estimate the probability that our method missed peaks (spatial: 0.12, temporal: 0.18) or detected false peaks (spatial: 0.11, temporal: 0.37) due to data gaps and showed that our approach remains useful even for sparse and/or sporadic location data. Our study presents a generalizable approach to evaluating migratory connectivity across the full annual cycle that can be used to focus migratory bird conservation towards places and times of the annual cycle where populations are more likely to be limited.

Hoary bats (Lasiurus cinereus) and silver-haired bats (Lasionycteris noctivagans) are species of conservation concern because of the documented annual mortality that occurs at wind energy facilities. Several recent studies have predicted continental-scale declines of hoary bat populations due to interactions with wind turbines. We predicted a decrease in captures at a summer site over 20 years where researchers have captured bats using generally consistent methods. We developed a hierarchical Bayesian model to estimate the relative change in the expected number of captures while controlling for time of year, temperature, and netting effort. We found no decrease in the number of captures for either species. We suggest that the lack of decrease observed at our study site may be a result of compensatory immigration, despite potential broader-scale population declines.

Seasonal and daily fluctuations in environmental temperature can affect the fitness of endotherms by increasing metabolic costs and energetic requirements. Consequently, some species adopt strategies that function to minimize costs, including minor circadian fluctuations in body temperature (Tb) and facultative reductions in Tb, known as heterothermy. The geographic and taxonomic patterns of variation in Tb are poorly-known, especially in the Neotropics. We investigated the diurnal variation in Tb of small birds inhabiting high-elevation Neotropical montane forests which must cope with predictably cool nighttime temperatures. Two-thirds of the individuals we measured lowered their Tb at night, and changes were greater when differences between daytime and nighttime ambient temperatures were greater. Our study expands the taxonomic and geographic scope of documented thermoregulatory flexibility in birds by demonstrating that even in the Neotropics, some montane birds may routinely adopt energy-saving physiological strategies. Such data are important to understanding and interpreting biogeographic patterns and behavior of tropical birds.

Plasma metabolite concentrations can be used to understand nutritional status and foraging behavior across ecological contexts including prehibernation fattening, migration refueling, and ...

Many species use stored energy to hibernate through periods of resource limitation. Hibernation, a physiological state characterized by depressed metabolism and body temperature, is critical to winter survival and reproduction, and therefore has been extensively quantified and modeled. Hibernation consists of alternating phases of extended periods of torpor (low body temperature, low metabolic rate), and energetically costly periodic arousals to normal body temperature. Arousals consist of multiple phases: warming, euthermia, and cooling. Warming and euthermic costs are regularly included in energetic models, but although cooling to torpid body temperature is an important phase of the torpor-arousal cycle, it is often overlooked in energetic models. When included, cooling cost is assumed to be 67% of warming cost, an assumption originally derived from a single study that measured cooling cost in ground squirrels. Since this study, the same proportional value has been assumed across a variety of hibernating species. However, no additional values have been derived. We derived a model of cooling cost from first principles and validated the model with empirical energetic measurements. We compared the assumed 67% proportional cooling cost with our model-predicted cooling cost for 53 hibernating mammals. Our results indicate that using 67% of warming cost only adequately represents cooling cost in ground squirrel-sized mammals. In smaller species, this value overestimates cooling cost and in larger species, the value underestimates cooling cost. Our model allows for the generalization of energetic costs for multiple species using species-specific physiological and morphometric parameters, and for predictions over variable environmental conditions.

Disease results from interactions among the host, pathogen, and environment. Inoculation trials can quantify interactions among these players and explain aspects of disease ecology to inform management in variable and dynamic natural environments. White-nose Syndrome, a disease caused by the fungal pathogen, Pseudogymnoascus destructans (Pd), has caused severe population declines of several bat species in North America. We conducted the first experimental infection trial on the tri-colored bat, Perimyotis subflavus, to test the effect of temperature and humidity on disease severity. We also tested the effects of temperature and humidity on fungal growth and persistence on substrates. Unexpectedly, only 37% (35/95) of bats experimentally inoculated with Pd at the start of the experiment showed any infection response or disease symptoms after 83 days of captive hibernation. There was no evidence that temperature or humidity influenced infection response. Temperature had a strong effect on fungal growth on media plates, but the influence of humidity was more variable and uncertain. Designing laboratory studies to maximize research outcomes would be beneficial given the high costs of such efforts and potential for unexpected outcomes. Understanding the influence of microclimates on host–pathogen interactions remains an important consideration for managing wildlife diseases, particularly in variable environments.

Energy conservation has long been a focal point in hibernation research. A long-standing assumption is that ambient temperature (Ta) largely defines the rate of energy expenditure because of well-known relationships between Ta, metabolic rate and frequency of arousal from torpor. Body condition and humidity also affect energy expenditure but are usually considered secondary factors. We held tricolored bats (Perimyotis subflavus) in captivity under multiple environmental conditions to directly compare the importance of Ta, fat mass and humidity for hibernation energy expenditure. Fat mass was the best predictor of female mass loss, followed by Ta and humidity. However, males had less fat and adopted a more energetically conservative hibernation strategy. Our results demonstrate that understanding the evolution of behavior, physiology and ecology of hibernation requires disentangling the relative contributions of multiple drivers of hibernation energetics, and that Ta is not always the most important factor driving energy expenditure.

Climate change and disease are threats to biodiversity that may compound and interact with one another in ways that are difficult to predict. White-nose syndrome (WNS), caused by a cold-loving fungus (Pseudogymnoascus destructans), has had devastating impacts on North American hibernating bats, and impact severity has been linked to hibernaculum microclimate conditions. As WNS spreads across the continent and climate conditions change, anticipating these stressors’ combined impacts may improve conservation outcomes for bats. We build on the recent development of winter species distribution models for five North American bat species, which used a hybrid correlative-mechanistic approach to integrate spatially explicit winter survivorship estimates from a bioenergetic model of hibernation physiology. We apply this bioenergetic model given the presence of P. destructans , including parameters capturing its climate-dependent growth as well as its climate-dependent effects on host physiology, under both current climate conditions and scenarios of future climate change. We then update species distribution models with the resulting survivorship estimates to predict changes in winter hibernacula suitability under future conditions. Exposure to P. destructans is generally projected to decrease bats’ winter occurrence probability, but in many areas, changes in climate are projected to lessen the detrimental impacts of WNS. This rescue effect is not predicted for all species or geographies and may arrive too late to benefit many hibernacula. However, our findings offer hope that proactive conservation strategies to minimize other sources of mortality could allow bat populations exposed to P. destructans to persist long enough for conditions to improve.

Multidisciplinary approaches to conservation and wildlife management are often effective in addressing complex, multi-factor problems. Emerging fields such as conservation physiology and conservation behaviour can provide innovative solutions and management strategies for target species and systems. Sensory ecology combines the study of ‘how animals acquire’ and process sensory stimuli from their environments, and the ecological and evolutionary significance of ‘how animals respond’ to this information. We review the benefits that sensory ecology can bring to wildlife conservation and management by discussing case studies across major taxa and sensory modalities. Conservation practices informed by a sensory ecology approach include the amelioration of sensory traps, control of invasive species, reduction of human–wildlife conflicts and relocation and establishment of new populations of endangered species. We illustrate that sensory ecology can facilitate the understanding of mechanistic ecological and physiological explanations underlying particular conservation issues and also can help develop innovative solutions to ameliorate conservation problems.

White‐nose syndrome (WNS) has decimated hibernating bat populations across eastern and central North America for over a decade. Disease severity is driven by the interaction between bat characteristics, the cold‐loving fungal agent, and the hibernation environment. While we further improve hibernation energetics models, we have yet to examine how spatial heterogeneity in host traits is linked to survival in this disease system. Here, we develop predictive spatial models of body mass for the little brown myotis (Myotis lucifugus) and reassess previous definitions of the duration of hibernation of this species. Using data from published literature, public databases, local experts, and our own fieldwork, we fit a series of generalized linear models with hypothesized abiotic drivers to create distribution‐wide predictions of prehibernation body fat and hibernation duration. Our results provide improved estimations of hibernation duration and identify a scaling relationship between body mass and body fat; this relationship allows for the first continuous estimates of prehibernation body mass and fat across the species' distribution. We used these results to inform a hibernation energetic model to create spatially varying fat use estimates for M. lucifugus. These results predict WNS mortality of M. lucifugus populations in western North America may be comparable to the substantial die‐off observed in eastern and central populations., White‐nose syndrome disease severity is driven by the interaction between bat characteristics, the cold‐loving fungal agent, and the hibernation environment. Here, we develop predictive spatial models of body mass for the little brown myotis (Myotis lucifugus) and reassess previous definitions of the duration of hibernation of this species. Our results provide improved estimations of hibernation duration and identify a scaling relationship between body mass and body fat; this relationship allows for the first continuous estimates of prehibernation body mass and fat across the species' distribution.

The first radiotelemetry study of bats was published in 1967, nearly coinciding with the first meeting in 1970 of bat biologists that evolved into the North American Society for Bat Research. Thus, NASBR provides a useful lens to assess the maturation of how this technology has been used in bat research. Researchers may view this developmental process as a purely technological one, as transmitters and receivers have improved dramatically over the last 50 years. However, there has also been growth in the scientific use of radiotracking to do bat research. The earliest studies were question driven and made innovative use of radiotelemetry to answer questions of biological theory previously beyond reach. We suggest that through the 1980s and 1990s there was a technology-driven period, with ever-improving transmitters increasing the number of species within the realm of study. However, researchers also continued to find new types of questions that could be addressed with standard equipment. Finally (and coinciding with the previous period), there has been a shift towards using biotelemetry to address completely different types of questions (e.g., physiological and biophysical). Radiotelemetry has clearly been a boon to bat research, which has allowed us to assess aspects of the ecology, physiology, and behavior of bats that would have otherwise been inaccessible. We look forward to the next 50 years of technological improvements and novel research using radiotracking methods.

Species with broad geographic ranges may experience varied environmental conditions throughout their range leading to local adaptation. Variation among populations reflects potential adaptability or plasticity, with implications for populations impacted by disease, climate change, and other anthropogenic influences. However, behavior may counteract divergent selection among populations. We studied intraspecific variation in hibernation physiology of Myotis lucifugus (little brown myotis) and Corynorhinus townsendii (Townsend’s big-eared bat), two species of bats with large geographic ranges. We studied M. lucifugus at three hibernacula which spanned a latitudinal gradient of 1500 km, and C. townsendii from 6 hibernacula spread across 1200 km latitude and 1200 km longitude. We found no difference in torpid metabolic rate among populations of either species, nor was there a difference in the effect of ambient temperature among sites. Evaporative water loss was similar among populations of both species, with the exception of one C. townsendii pairwise site difference and one M. lucifugus site that differed from the others. We suggest the general lack of geographic variation is a consequence of behavioral microhabitat selection. As volant animals, bats can travel relatively long distances in search of preferred microclimates for hibernation. Despite dramatic macroclimate differences among populations, hibernating bats are able to find preferred microclimate conditions within their range, resulting in similar selection pressures among populations spread across wide geographic ranges.

Caves and other subterranean features provide unique environments for many species. The importance of cave microclimate is particularly relevant at temperate latitudes where bats make seasonal use of caves for hibernation. White‐nose syndrome (WNS), a fungal disease that has devastated populations of hibernating bats across eastern and central North America, has brought renewed interest in bat hibernation and hibernaculum conditions. A recent review synthesized current understanding of cave climatology, exploring the qualitative relationship between cave and surface climate with implications for hibernaculum suitability. However, a more quantitative understanding of the conditions in which bats hibernate and how they may promote or mediate WNS impacts is required. We compiled subterranean temperatures from caves and mines across the western United States and Canada to (1) quantify the hypothesized relationship between mean annual surface temperature (MAST) and subterranean temperature and how it is influenced by measurable site attributes, and (2) use readily available gridded data to predict and continuously map the range of temperatures that may be available in caves and mines. Our analysis supports qualitative predictions that subterranean winter temperatures are correlated with MAST, that temperatures are warmer and less variable farther from the surface, and that even deep within‐cave temperatures tend to be lower than MAST. Effects of other site attributes (e.g., topography, vegetation, and precipitation) on subterranean temperatures were not detected. We then assessed the plausibility of model‐predicted temperatures using knowledge of winter bat distributions and preferred hibernaculum temperatures. Our model unavoidably simplifies complex subterranean environments and is not intended to explain all variability in subterranean temperatures. Rather, our results offer researchers and managers improved broad‐scale estimates of the geographic distribution of potential hibernaculum conditions compared to reliance on MAST alone. We expect this information to better support range‐scale estimation of winter bat distributions and projection of likely WNS impacts across the west. We suggest that our model predictions should serve as hypotheses to be further tested and refined as additional data become available.

Research Highlights: Seasonal variation in environmental conditions coinciding with reproductive and energetic demands might result in seasonal differences in species-specific habitat use. We studied a winter assemblage of insectivorous bats and found that species acted as habitat generalists during winter compared to expectations based on the summer active season. Background and Objectives: In temperate regions, seasonal fluctuations in resource availability might restructure local bat assemblages. Initially perceived to only hibernate or migrate to avoid adverse winter conditions, temperate insectivorous bats appear to also employ intermediate overwintering strategies, as a growing body of literature suggests that winter activity is quite prevalent and even common in some lower latitude areas. However, to date, most studies have exclusively assessed habitat associations during summer. Because habitat use during summer is strongly influenced by reproduction, we hypothesized that habitat associations might differ during the non-reproductive winter period. We used acoustic monitoring to assess the habitat associations of bats across a managed pine landscape in the southeastern United States. Materials and Methods: During the winters of 2018 and 2019, we deployed acoustic detectors at 72 unique locations to monitor bat activity and characterized vegetation conditions at two scales (microhabitat and landscape). We used linear mixed models to characterize species-specific activity patterns associated with different vegetation conditions. Results: We found little evidence of different activity patterns during winter. The activity of three species (hoary bat: Lasiurus cinereus; southeastern myotis: Myotis austroriparius; and tricolored bat: Perimyotis subflavus) was not related to vegetation variables and only modest relationships were evident for four other species/groups (big brown bat: Eptesicus fuscus; eastern red bat: L. borealis; Seminole bat: L. seminolus; evening bat: Nycticeius humeralis; and Brazilian free-tailed bat: Tadarida brasiliensis). Conclusions: During winter, the bats in our study were active across the landscape in various cover types, suggesting that they do not exhibit the same habitat associations as in summer. Therefore, seasonal differences in distributions and habitat associations of bat populations need to be considered so that effective management strategies can be devised that help conserve bats year round.

Fungal diseases of wildlife typically manifest as superficial skin infections but can have devastating consequences for host physiology and survival. White-nose syndrome (WNS) is a fungal skin disease that has killed millions of hibernating bats in North America since 2007. Infection with the fungus Pseudogymnoascus destructans causes bats to rewarm too often during hibernation, but the cause of increased arousal rates remains unknown. On the basis of data from studies of captive and free-living bats, two mechanistic models have been proposed to explain disease processes in WNS. Key predictions of both models are that WNS-affected bats will show 1) higher metabolic rates during torpor (TMR) and 2) higher rates of evaporative water loss (EWL). We collected bats from a WNS-negative hibernaculum, inoculated one group with P. destructans, and sham-inoculated a second group as controls. After 4 mo of hibernation, TMR and EWL were measured using respirometry. Both predictions were supported, and our data suggest that infected bats were more affected by variation in ambient humidity than controls. Furthermore, disease severity, as indicated by the area of the wing with UV fluorescence, was positively correlated with EWL, but not TMR. Our results provide the first direct evidence that heightened energy expenditure during torpor and higher EWL independently contribute to WNS pathophysiology, with implications for the design of potential treatments for the disease.

While some bats cover long distances during migration, moving thousands of kilometers, most migratory bats are considered regional migrants, thought to move relatively short distances ( 100 km, suggesting that longer-distance movements may be outliers. In autumn, only two bats visited multiple known hibernacula, and after swarming, some females moved > 100 km to areas without known hibernacula. Common generalizations about regional migrant movements may not be representative of population behavior and care should be taken with respect to management decisions based on those assumptions.

Plasma metabolite analysis is frequently used to assess the energetic state and energy intake of birds. Plasma β-hydroxybutyrate (BUTY) is a common metabolite used in these studies, and is correlated with fasting and mass loss. BUTY is typically quantified in laboratory assays that are costly, time-consuming, and prone to human error. We tested the accuracy and precision of a field-ready handheld BUTY meter. We compared BUTY concentration values obtained in the laboratory and with the handheld meter in plasma samples from 19 Grasshopper Sparrows (Ammodramus savannarum), and assessed precision with repeat analysis of a single sample. The handheld meter reported BUTY concentrations in

Large numbers of migratory bats are killed every year at wind energy facilities. However, population-level impacts are unknown as we lack basic demographic information about these species. We investigated whether fatalities at wind turbines could impact population viability of migratory bats, focusing on the hoary bat ( Lasiurus cinereus ), the species most frequently killed by turbines in North America. Using expert elicitation and population projection models, we show that mortality from wind turbines may drastically reduce population size and increase the risk of extinction. For example, the hoary bat population could decline by as much as 90% in the next 50 years if the initial population size is near 2.5 million bats and annual population growth rate is similar to rates estimated for other bat species (λ = 1.01). Our results suggest that wind energy development may pose a substantial threat to migratory bats in North America. If viable populations are to be sustained, conservation measures to reduce mortality from turbine collisions likely need to be initiated soon. Our findings inform policy decisions regarding preventing or mitigating impacts of energy infrastructure development on wildlife.

Hibernation consists of extended durations of torpor interrupted by periodic arousals. The ‘dehydration hypothesis’ proposes that hibernating mammals arouse to replenish water lost through evaporation during torpor. Arousals are energetically expensive, and increased arousal frequency can alter survival throughout hibernation. Yet we lack a means to assess the effect of evaporative water loss (EWL), determined by animal physiology and hibernation microclimate, on torpor bout duration and subsequent survival. White-nose syndrome (WNS), a devastating disease impacting hibernating bats, causes increased frequency of arousals during hibernation and EWL has been hypothesized to contribute to this increased arousal frequency. WNS is caused by a fungus, which grows well in humid hibernaculum environments and damages wing tissue important for water conservation. Here, we integrated the effect of EWL on torpor expression in a hibernation energetics model, including the effects of fungal infection, to determine the link between EWL and survival. We collected field data forMyotis lucifugus, a species that experiences high mortality from WNS, to gather parameters for the model. In saturating conditions we predicted healthy bats experience minimal mortality. Infected bats, however, suffer high fungal growth in highly saturated environments, leading to exhaustion of fat stores before spring. Our results suggest that host adaptation to humid environments leads to increased arousal frequency from infection, which drives mortality across hibernaculum conditions. Our modified hibernation model provides a tool to assess the interplay between host physiology, hibernaculum microclimate, and diseases such as WNS on winter survival.

Processes associated with recovery of survivors are understudied components of wildlife infectious diseases. White-nose syndrome (WNS) in bats provides an opportunity to study recovery of disease survivors, understand implications of recovery for individual energetics, and assess the role of survivors in pathogen transmission. We documented temporal patterns of recovery from WNS in little brown bats (Myotis lucifugus) following hibernation to test the hypotheses that: 1) recovery of wing structure from WNS matches a rapid timescale (i.e., about 30 days) suggested by data from free-ranging bats; 2) torpor expression plays a role in recovery; 3) wing physiological function returns to normal alongside structural recovery; and 4) pathogen loads decline quickly during recovery. We collected naturally infected bats at the end of hibernation, brought them into captivity, and quantified recovery over 40 days by monitoring body mass, wing damage, thermoregulation, histopathology of wing biopsies, skin surface lipids, and fungal load. Most metrics returned to normal within 30 days although wing damage was still detectable at the end of the study. Torpor expression declined overall throughout the study but bats expressed relatively shallow torpor bouts, with a plateau in minimum skin temperature, during intensive healing between about days 8 and 15. Pathogen loads were nearly undetectable after the first week of the study , but some bats were still detectably infected at day 40. Our results suggest that healing bats face severe energetic imbalance during early recovery from direct costs of healing and reduced foraging efficiency. Management of WNS should not rely solely on actions during winter but should also aim to support energy balance of recovering bats during spring and summer.

As small, flying, mammalian endotherms, insectivorous bats are adapted to operate at high levels of energy expenditure. In response to seasonally variable challenges, we predicted that bats should balance energy budgets by flexibly adjusting aspects of their physiology or behavior in ways that elevate metabolic capacity. We examined variation in energy storage and pathways for oxidative metabolism in Brazilian free-tailed bats (Tadarida brasiliensis) related to estimated costs associated with reproduction and migration. We collected pectoral muscle and liver from female T. brasiliensis at six time points during the summer and fall and measured changes in the activity of four enzymes involved with lipid metabolism. Body mass varied substantially with life-cycle stage, suggesting that rapid accumulation and use of fat stores occurs in response to current and anticipated energy demands. Catabolic enzyme activity (carnitine palmitoyl transferase [CPT], 3-hydroxyacyl-CoA dehydrogenase [HOAD], and citrate synthase [CS]) in the muscle was increased during lactation compared with early pregnancy but exhibited no change before fall migration. While there was no temporal change in lipid biosynthetic capacity in the liver, fatty acid synthase activity was negatively correlated with body mass. Variation in body mass and enzyme activity in T. brasiliensis during the summer suggests that stored energy is mobilized and lipid oxidative capacity is increased during periods of increased demand and that lipid biosynthetic capacity is increased with depletion of fat stores. These results suggest that bats are able to flexibly adjust metabolic capacity based on energy requirement to maintain energy balance despite high levels of expenditure.

Plasma metabolite concentrations can be used to understand nutritional status and foraging behavior across ecological contexts including prehibernation fattening, migration refueling, and variation in foraging habitat quality. Generally, high plasma concentrations of the ketone β-hydroxybutyrate, a product of fat catabolism, indicate fasting, while triglycerides indicate recent feeding and fat accumulation. In recent studies of insectivorous bats, triglyceride concentration increased after feeding as expected, but β-hydroxybutyrate also unexpectedly increased rather than decreased. An aerial-hawking foraging strategy is energetically demanding, and thus it has been hypothesized that foraging by insectivorous bats requires catabolism of stored fat. We tested this hypothesis by quantifying plasma β-hydroxybutyrate and triglyceride concentration following feeding in little brown bats (

During autumn, temperate bats must deposit fat stores for hibernation. Populations at high latitudes face four challenges: a shorter active season and shorter nights during the active season (less time to accumulate fat), a longer hibernation period (larger fat store needed), and colder nights (reduced prey availability). Mating also occurs during the prehibernation period, placing time constraints for mating and fattening on northern populations. We tested the hypothesis that these factors constrain prehibernation foraging in northern populations of little brown bats (Myotis lucifugus (Le Conte, 1831)). We measured plasma triglyceride concentration to study prehibernation fueling rates of a population near the northern range limit of the species and compared our results with previously published results from a more southern population. In contrast to bats at the lower latitude, we found consistently low concentrations of plasma triglycerides, indicating a low fuelling rate throughout the prehibernation period. However, despite an apparently low fuelling rate, bats achieved a substantially greater body mass. The discrepancy between populations suggests that environmental constraints lead northern populations to employ different behavioural or physiological strategies to prepare for hibernation.

Summary The management of infectious diseases is an important conservation concern for a growing number of wildlife species. However, effective disease control in wildlife is challenging because feasible management options are often lacking. White-nose syndrome (WNS) is an infectious disease of hibernating bats that currently threatens several North American species with extinction. Currently, no effective treatments exist for WNS. We conducted a laboratory experiment to test the efficacy of probiotic treatment with Pseudomonas fluorescens, a bacterium that naturally occurs on bats, to reduce disease severity and improve survival of little brown bats Myotis lucifugus exposed to Pseudogymnoascus destructans, the fungal pathogen that causes WNS. We found that application of the probiotic bacteria at the time of fungal infection reduced several measures of disease severity and increased survival, whereas bacterial treatment prior to pathogen exposure had no effect on survival and worsened disease severity. Synthesis and applications. Our results suggest that probiotic treatment with Ps. fluorescens has potential for white-nose syndrome disease management, but the timing of application is critical and should coincide with natural exposure of bats to P. destructans. These results add to the growing knowledge of how natural host microbiota can be implemented as a biocontrol treatment to influence disease outcomes.

Common Nighthawks (Chordeiles minor) are aerial insectivores that often forage over water, at high speeds, and sometimes at high densities. Foraging nighthawks have regularly been observed flying < 1 m from the surface of water. under these circumstances, navigation errors or mid-air collisions could result in birds falling into the water, with the risk of drowning. We report two observations of Common Nighthawks that fell into a river and were able to take off from the surface of the water easily without any noticeable detrimental effects.

As organisms face variation in energetic challenges and physiological demands, they often respond with reversible changes in behavior, physiology, and morphology, described as phenotypic flexibility. From the magnitude of phenotypic change, we can infer the energetic challenges of different life stages. We studied phenotypic flexibility in a population of reproductive and pre-migratory female insectivorous bats (Tadarida brasiliensis). While female reproductive demands are well described in insectivorous bats, there are questions regarding the demands of migration. Our objective was to measure phenotypic flexibility to assess the cost of autumn migration compared to reproduction in an insectivorous bat. We measured plasma triglycerides to quantify foraging rate, and body composition (body mass and individual organ mass) of T. brasiliensis throughout the summer season (from arrival in spring through pre-migration/migration departure in autumn) according to the female reproductive cycle. We found phenotypic changes during pre-migration/migration similar to periods of high-energy demand during reproduction (e.g., late pregnancy and lactation). Most notably, bats weighed as much during peak pregnancy, as they did during migration, and the rapid mass gain from post-lactation through the migratory period was due to a combination of hyperphagia and hypertrophy of digestive organs. Our results indicate that energetic demands incurred during migration are similar to those during reproduction and emphasize the energetic challenges of migration.

White-nose syndrome is a fungal disease that has killed millions of hibernating bats. One symptom is electrolyte depletion. We tested whether providing an electrolyte supplement, a potentially simple and cost-effective conservation intervention, to hibernating bats would reduce disease severity. The treatment was not effective and may have increased fungal growth., Fungi are increasingly recognised as harmful pathogens of wildlife. White-nose syndrome (WNS) is a fungal disease that has killed millions of hibernating bats in North America. High mortality has driven research to identify management strategies for the disease. Increased energy expenditure and fat depletion, as well as fluid loss, hypotonic dehydration and electrolyte depletion appear to be key aspects of WNS pathophysiology. Bats with WNS spend energy too quickly and also lose fluids containing water and electrolytes from lesions on exposed skin surfaces. During periodic arousals, bats often drink water but, in most of the WNS-affected area, food is not available during winter and, therefore, they cannot maintain energy balance or replace lost electrolytes. Therefore, providing a liquid caloric/electrolyte/nutrient supplement could be useful for treating WNS. We studied captive, hibernating little brown bats (Myotis lucifugus) to test whether providing supplemental energy and electrolytes (a 1:1 dilution of unflavoured Pedialyte) to hibernating bats could reduce severity of WNS symptoms and increase survival. Infected bats in the Pedialyte-supplemented group generally avoided the Pedialyte and preferentially drank plain water. We did not observe any differences in survival, arousal frequency or blood chemistry, but bats in the Pedialyte-supplemented group had higher fungal load and more UV fluorescence than the control group that was only provided with water. Supplemental electrolytes would be an attractive management strategy because of their low cost and logistic feasibility but our results suggest this approach would be ineffective. However, it could be useful to conduct preference experiments with multiple dilutions and/or flavours of electrolyte solution. Although they did not prefer Pedialyte in our experiment, bats in the hand readily drink it and electrolyte supplementation remains an important tool for rehabilitation of captive bats recovering from WNS and other causes of dehydration.